Explain the selection of switch in network video monitoring system in detail
With the increasing use of high-definition cameras, how to choose the right switch that meets the performance of the overall network architecture has also become a very important role in the development of the high-definition monitoring system's early program and project quotation. A suitable switch can not only play the function of monitoring network but also effectively reduce the waste of resources.
Key switch parameters
Backplane bandwidth
The backplane bandwidth is the maximum amount of data that can be transmitted between the switch interface processor or interface card and the data bus. The backplane bandwidth marks the total data exchange capability of the switch, and the unit is Gbps, also known as the exchange bandwidth. The higher the bandwidth of the backplane of a switch, the stronger the data processing capability.
Backplane bandwidth calculation method: Number of ports * port speed *2= backplane bandwidth, take the CS1024-12GF12GE as an example, this switch has 12 gigabit electrical ports, 12 gigabit SFP, backplane bandwidth =24*1000*2/1000=48Gbps.
If the backplane bandwidth is less than or equal to the nominal backplane bandwidth, the switching device has a linear speed on the backplane bandwidth, which is also called non-blocking.
Forwarding performance (sum of packet forwarding rates of ports)
Packet forwarding rate, also known as port throughput, refers to the ability of a router to forward packets on a certain port, usually measured in pps (packets per second). Generally speaking, the packet forwarding rate of low-end routers is only a few K to dozens of Kpps, while high-end routers can reach tens of Mpps (millions of packets per second) or even hundreds of Mpps. Calculation method of packet forwarding rate: Number of fully configured Gigabit ports x 1.488Mpps+ Number of fully configured 100 gigabit ports x 0.1488Mpps= Packet forwarding rate (The theoretical throughput of a Gigabit port with 64 bytes is 1.488Mpps, and that of a 100 gigabit port with 64 bytes is 0.1488Mpps). Taking the Huacheng Century CS1018-16F2GE as an example, the switch has 16 100 Mbit optical ports and 2 gigabit electrical ports. Packet forwarding rate =16*0.1488Mpps+2*1.488Mpps=5.3568Mpps.
The whole machine forwarding rate is less than the nominal packet forwarding rate, then the switching equipment is line speed on the whole machine forwarding, also known as no blocking.
Switch selection suggestion
For a set of large and medium-sized network monitoring system, the switch configuration is generally composed of three parts: access layer, aggregation layer and core layer.
Access layer:
You can select 8 or 16 ordinary 100 Mbit/s switches. It is recommended that the number of cameras on the access switches be controlled to 6 to 10.
The actual bandwidth of our commonly used switches is 50%-70% of the theoretical value, so the actual bandwidth of a 100 megabit port is 50M-70M. 4M x 12=48M. Therefore, it is recommended that a 100 Mbit access switch connect to a maximum of 12 720P network cameras. At the same time, considering that the current network monitoring uses dynamic coding, the peak stream of the camera may exceed 4M bandwidth, while considering the bandwidth redundancy design, so a 100 Mbit access switch is best controlled within 8, more than 8 are recommended to use gigabit port.
Convergence layer:
A Layer 2 switch with thousands of upload ports can be selected, which has higher performance requirements than an access switch. The 100 Mbit/s port of the switch is connected to the Ethernet switch, and the number of cameras on the Ethernet port and the core switch of the monitoring center and the aggregation switch should be controlled to about 30.
Based on the 4M code stream of the 720P network camera, there are six 720P network cameras on each front-end access layer switch, and the aggregation switch is connected to five access layer switches. The total bandwidth of the aggregation layer switch is 4M x 6 x 5=120M. Therefore, the aggregation switch and core switch must be connected to gigabit ports.
Core layer:
The core switch is the core of the entire digital monitoring system, connect the aggregation switch, connect the video surveillance platform, storage server, digital matrix and other devices, it is recommended to choose the three-layer full gigabit core switch, the number of cameras more than 150 consider the three-layer 10-gigabit core switch.
Give an example
If 5 IPCAMs are connected to a switch, we generally use an 8-port switch, then does this 8-port switch meet the requirements? So let's calculate at least three aspects of this switch's capabilities.
1. Backplane bandwidth: Port number x port speed x 2= backplane bandwidth, 8*100*2=1.6Gbps/S
2. Packet switching rate: number of ports * port speed /1000*1.488Mpps= packet switching rate, 8*100/1000*1.488=1.20Mpps/S, some switches sometimes calculate the packet switching rate can not meet this requirement, then it is non-line speed switch, when carrying out large capacity quantity throughput, easy to cause delay.
3. Cascade port bandwidth: IPCAM stream * number = minimum bandwidth of upload port,4.5*5=22.5Mbps/S, generally, when IPCAM bandwidth exceeds 45Mbps, it is recommended to use 1000M cascade port.
Points to note when selecting:
1, in order to facilitate management, optional WEB management switch;
2, due to the large video traffic, line speed switch can be selected;
3, video data has the characteristics of sudden, the larger the switch cache, the better;
4, switch flow control function;
5. Aggregation switches and core switches are recommended to choose manufacturers with stable product quality and strong technical service capabilities.